Energy exchange assembly with microporous membrane

ABSTRACT

An energy exchange assembly may include one or more membrane panels. The one or more membrane panels may include a microporous membrane that has a pore size between 0.02 and 0.3 micrometers (μm) and a porosity between 45% and 80%. Optionally, the energy exchange assembly may further include a plurality of spacers that define air channels. The air channels may be configured to receive air streams therethrough. Each of the one or more membrane panels may be disposed between two spacers. The one or more membrane panels may be configured to allow a transfer of sensible energy and latent energy across the one or more membrane panels between the air channels.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application relates to and claims priority benefit from U.S.Provisional Patent Application No. 61/784,638, entitled “Air-To-AirEnergy Recovery Core With Microporous Membrane,” filed Mar. 14, 2013,which is hereby expressly incorporated by reference in its entirety.

BACKGROUND OF THE DISCLOSURE

Embodiments of the present disclosure generally relate to an energyexchange assembly, such as an energy recovery core, that incorporates amicroporous membrane.

Energy exchange assemblies are used to transfer energy, such as sensibleand/or latent energy, between fluid streams. For example, air-to-airenergy recovery cores are used in heating, ventilation, and airconditioning (HVAC) applications to transfer heat (sensible energy) andmoisture (latent energy) between two airstreams. A typical energyrecovery core is configured to precondition outdoor air to a desiredcondition through the use of air that is exhausted out of the building.For example, outside or supply air is channeled through the energyrecovery core in proximity to exhaust air. Energy between the supply andexhaust air streams is transferred therebetween. In the winter, forexample, cool and dry outside air is warmed and humidified throughenergy transfer with the warm and moist exhaust air. As such, thesensible and latent energy of the outside air is increased, while thesensible and latent energy of the exhaust air is decreased. The energyrecovery core typically reduces post-conditioning of the supply airbefore it enters the building, thereby reducing overall energy use ofthe system.

Air-to-air recovery cores may include a membrane through which heat andmoisture are transferred between air streams. The membrane may beseparated from adjacent membranes using a spacer. In an energy recoverycore, the amount of heat transferred is generally determined by atemperature difference and convective heat transfer coefficient of thetwo air streams, as well as the material properties of the membrane. Theamount of moisture transferred in the core is generally governed by ahumidity difference and convective mass transfer coefficients of the twoair streams, but also depends on the material properties of themembrane.

One known type of membrane used in an energy recovery core is anon-porous hygroscopic membrane. This membrane has a hygroscopic coatingwhich is bonded to a resin or paper-like substrate material. Thehygroscopic coating is used to drive moisture transfer through themembrane, while the substrate is used for an added layer of support. Thehygroscopic coating may be configured to allow very little air transferthrough the membrane at standard operating differential pressures.However, the ability for the membrane to transfer moisture typicallydepends on the relative humidity of the air. In a very humidenvironment, hygroscopic membranes have a low vapor diffusionresistance. In low humidity environments, however, hygroscopic membraneshave a high vapor diffusion resistance. As such, an energy recovery coreincluding such membranes generally exhibits a large change in latenteffectiveness between heating and cooling conditions.

Another known type of membrane used in an energy recovery core is acomposite polymer membrane. The composite polymer membrane has a thinvapor-promoting polymer film coated on a porous polymer substrate. Thepolymer film is used to drive moisture transfer through the membrane andprohibit airflow through the membrane at standard operating differentialpressures. The porous polymer substrate may be used to reinforce themembrane while allowing the transfer of vapor therethrough. In addingand bonding multiple polymer layers together, however, the resistance tomoisture transfer (i.e., the vapor diffusion resistance) through themembrane increases. Depending on the polymer film used in the compositemembrane, the vapor diffusion resistance may be highly dependent on therelative humidity of the air streams.

SUMMARY OF THE DISCLOSURE

Certain embodiments of the present disclosure provide an energy exchangeassembly that may include one or more membrane panels. The one or moremembrane panels may include a microporous membrane that has a pore sizebetween 0.02 and 0.3 micrometers (μm) and a porosity between 45% and80%.

Optionally, the energy exchange assembly may further include a pluralityof spacers that define air channels. The air channels may be configuredto receive air streams therethrough. Each of the one or more membranepanels may be disposed between two spacers. The one or more membranepanels may be configured to allow a transfer of sensible energy andlatent energy across the one or more membrane panels between the airchannels. Optionally, the pore size of the microporous membrane may bebetween 0.04 and 0.2 μm. The porosity of the microporous membrane may bebetween 50% and 75%. The microporous membrane may have a vapor diffusionresistance below 40 seconds/meter (sec/m) and an air permeability below0.06 ft³/min/ft².

Certain embodiments of the present disclosure provide an energy exchangesystem that may include a supply air flow path configured to channelsupply air to an enclosed structure, a regeneration air flow pathconfigured to channel regeneration air from the enclosed structure to anoutside environment, and an energy exchange assembly disposed within thesupply air flow path and the regeneration air flow path. The energyexchange assembly may include a plurality of spacers and a plurality ofmembrane panels. Each membrane panel may include a microporous membranethat has a pore size between 0.02 and 0.3 micrometers (μm) and aporosity between 45% and 80%. Each of the spacers may be positionedbetween two of the membrane panels to define air channels through thespacer between the two membrane panels. The air channels may beconfigured to receive air streams therethrough. The membrane panels maybe configured to allow a transfer of sensible energy and latent energyacross the membrane panels between the air channels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a perspective top view of an energy exchangeassembly, according to an embodiment of the present disclosure.

FIG. 2 illustrates a perspective exploded top view of two adjacentlayers of the energy exchange assembly shown in FIG. 1, according to anembodiment of the present disclosure.

FIG. 3 illustrates an end view of two adjacent layers of the energyexchange assembly shown in FIG. 1, according to an embodiment of thepresent disclosure.

FIG. 4 illustrates a magnified microporous membrane of the energyexchange assembly shown in FIG. 1, according to an embodiment of thepresent disclosure.

FIG. 5 illustrates a graph plotting vapor diffusion resistance versusmean relative humidity for comparison between three membranes.

FIG. 6 illustrates a simplified schematic view of an energy exchangesystem operatively connected to an enclosed structure, according to anembodiment of the present disclosure.

Before the embodiments are explained in detail, it is to be understoodthat the disclosure is not limited in its application to the details ofconstruction and the arrangement of the components set forth in thefollowing description or illustrated in the drawings. The disclosure iscapable of other embodiments and of being practiced or being carried outin various ways. Also, it is to be understood that the phraseology andterminology used herein are for the purpose of description and shouldnot be regarded as limiting. The use of “including” and “comprising” andvariations thereof is meant to encompass the items listed thereafter andequivalents thereof as well as additional items and equivalents thereof.

DETAILED DESCRIPTION OF THE DISCLOSURE

The foregoing summary, as well as the following detailed description ofcertain embodiments will be better understood when read in conjunctionwith the appended drawings. As used herein, an element or step recitedin the singular and proceeded with the word “a” or “an” should beunderstood as not excluding plural of the elements or steps, unless suchexclusion is explicitly stated. Furthermore, references to “oneembodiment” are not intended to be interpreted as excluding theexistence of additional embodiments that also incorporate the recitedfeatures. Moreover, unless explicitly stated to the contrary,embodiments “comprising” or “having” an element or a plurality ofelements having a particular property may include additional suchelements not having that property.

FIG. 1 illustrates a perspective top view of an energy exchange assembly10, according to an embodiment of the present disclosure. The energyexchange assembly 10 may be an energy recovery core, a plate heatexchanger, or the like configured to transfer energy between fluidstreams, such as first and second air streams 12 and 14. As such, theenergy exchange assembly 10 may be an air-to-air energy recovery coreassembly.

The energy exchange assembly 10 may include a plurality of microporousmembranes 16 separated by spacers 18. The membranes 16 may be formed ofa microporous material that is configured to allow sensible and latentenergy to pass therebetween. The membranes 16 may be designed with apore size and a porosity that achieves a desired balance of airpermeability and vapor permeability. For example, the characteristics ofthe microporous membranes 16 may be designed to enhance the transfer ofvapor across the membranes 16 while also reducing the air transferacross the membranes 16. By stacking the membranes 16 and the spacers18, channels 19 are formed that allow the first and second air streams12 and 14 to pass through the energy exchange assembly 10.

The energy exchange assembly 10 may be oriented so that the first airstream 12 may be outside air that is to be conditioned, while the secondair stream 14 may be exhaust, return, or scavenger air that is used tocondition the outside air before the outside air is supplied todownstream HVAC equipment and/or an enclosed space as supply air. Heatand moisture may be transferred between the first and second air streams12 and 14 through the membranes 16 within the energy exchange assembly10.

The microporous membranes 16 and spacers 18 may be secured between outerupstanding brackets 20, a base 22, and a top wall 24. As shown, thebrackets 20 may generally be at the corners of the energy exchangeassembly 10. The base 22, the top wall 24, and the brackets 20 provide amain housing defining an internal chamber into which the membranes 16and the spacers 18 are secured.

The energy exchange assembly 10 may include a plurality of layers orlevels 26 which are vertically stacked along an elevation axis z. Eachlayer 26 may include a spacer 18 positioned between two microporousmembranes 16. One membrane 16 may be below the spacer 18, while theother membrane 16 in the layer 26 is disposed above the spacer 18. In anembodiment, the spacers 18 and membranes 16 are stacked in analternating pattern such that only one membrane 16 separates adjacentspacers 18. Thus, adjacent layers 26A, 26B may share one membrane 16.The spacers 18 in adjacent layers 26A, 26B may be oriented orthogonallyto each other such that the air channels 19 through the spacers 18channel the air in different directions. For example, the air channels19 in the layers 26A may be oriented parallel to an axis y, while theair channels 19 in the layers 26B may be oriented parallel to an axis x,which is perpendicular (or oriented at an acute angle) to the axis y.Thus, the levels 26A may be oriented to receive the second air stream 14at an inlet side 30 and direct the second air stream 14 to an outletside 31, while the levels 26B may be oriented to receive the first airstream 12 at an inlet side 32, which is perpendicular to the inlet side30, and direct the first air stream 12 to an outlet side 33, which isperpendicular to the outlet side 31. Therefore, the air stream 14,passing through the levels 26A, travels in a cross-flow direction withthe air stream 12 passing through the levels 26B. In this manner,sensible and/or latent energy may be exchanged between the levels 26Aand 26B.

For example, as shown in FIG. 1, the first air stream 12 may enter theinlet side 32 as cool, dry air. As the first air stream 12 passesthrough the energy exchange assembly 10, the temperature and humidity ofthe first stream 12 are both increased through energy transfer with thesecond air stream 14 that enters the energy exchange assembly 10 throughthe inlet side 30 as warm, moist air. Accordingly, the first air stream12 passes out of the outlet side 33 as warmer, moister air (as comparedto the first air stream 12 before passing into the inlet side 32), whilethe second air stream 14 passes out of the outlet side 31 as cooler,drier air (as compared to the second air stream 14 before passing intothe inlet side 30). In general, the temperature and humidity of thefirst and second air streams 12 and 14 passing through the levels 26Aand 26B tends to at least partially equilibrate with one another. Forexample, warm, moist air within the levels 26A is cooled and dried byheat exchange with the cooler, drier air in the levels 26B. Cool, dryair within the levels 26B is warmed and moistened by the warmer, coolerair within the levels 26A. As a result, the second air stream 14 thatpasses through the levels 26A may be cooler and drier after passingthrough the energy exchange assembly 10. Conversely, the first airstream 12 that passes through the levels 26B may be warmer and moisterafter passing through the energy exchange assembly 10.

FIG. 2 illustrates a perspective exploded top view of two adjacentlayers 26 of the energy exchange assembly 10 shown in FIG. 1, accordingto an embodiment of the present disclosure. The layers 26 includealternating spacers 18 and microporous membranes 16, which are stackedon top of each other in a layer stack 202. The microporous membranes 16may form a part of membrane panels 206, which are alternatively stackedwith the spacers 18. The membrane panels 206 may each include a sheet ofthe microporous membrane 16 and an outer frame 208 to which the membrane16 is attached, disposed, or integrated. The outer frame 208 may be aplastic or other polymer frame that retains the microporous membrane 16in a stretched or at least tight configuration within an inner space(not shown) defined by the frame 208. The frame 208 may engage thespacers 18 when assembling the layer stack 202. In an alternativeembodiment, the membrane panels 206 do not include an outer frame 208.

The microporous membranes 16 may include thin, porous sheets composed ofexpanded polytetrafluoroethylene (ePTFE), polypropylene (PP), nylon,polyvinylidene fluoride (PVDF), polyethersulfone (PES), combinationsthereof, or the like. The membranes 16 may be hydrophobic or hydrophilic(for example, if composed of nylon). The membranes 16 optionally may bemanufactured by a dry stretch process, a wet stretch process, or anotherprocess. In at least one embodiment, the membrane panels 206 may includea backing layer (not shown in FIG. 2) that is bonded to the microporousmembrane 16 to provide structural support to the membrane 16. Thebacking layer may be a spunbond non-woven or a non-woven mesh. Thebacking layer may be made from materials including polypropylene (PP),polyethylene (PE), polyester, nylon, fiberglass, and/or the like. Thebacking layer of the membrane panel 206 provides support to themicroporous membrane 16, making the membrane 16 stiffer and moredurable. In at least one embodiment, each backing layer is bonded to asingle sheet or layer of the microporous membrane 16 to form eachmembrane panel 206.

The spacers 18 may be formed of plastic, metal, or the like. As shown inFIG. 2, the spacers 18 include walls 210 that are aligned parallel toeach other, and connecting cross-bars 212 that structurally support thewalls 210. The air channels 19 are formed between adjacent walls 210 andextend along the length of the walls 210. For example, the walls 210 mayengage the membrane panels 206 above and below the spacer 18. The heightof the walls 210 may define the height of the channels 19. Thecross-bars 212 may have a small height relative to the walls 210 toprohibit the cross-bars 212 from impeding the flow of air through thechannels 19. In alternative embodiments, the spacers 18 may have variousother sizes and shapes. For example, the spacers may be corrugated withcurved, undulating walls or saw tooth angled walls instead of upstandingwalls.

During assembly of the layer stack 202, a lower spacer 18A is mounted ontop of a lower membrane panel 206A. A middle membrane panel 206B issubsequently mounted on top of the spacer 18A. An upper spacer 18B isthen mounted on the middle membrane panel 206B, and an upper membranepanel 206C is mounted on the upper spacer 18B. As used herein, relativeor spatial terms such as “top,” “bottom,” “upper,” “lower,” and “middle”are only used to distinguish the referenced elements and do notnecessarily require particular positions or orientations in the energyexchange assembly 10 (shown in FIG. 10) or in the surroundingenvironment of the energy exchange assembly 10. The stacking pattern maycontinue to produce an energy exchange assembly 10 of a desired height.In an embodiment, the upper spacer 18B is rotated 90° relative to thelower spacer 18A. Consequently, the channels 19 through the spacer 18Aare orthogonal to the channels 19 through the spacer 18B, so that airflows through the channels 19 of the adjacent layers 26A, 26B in across-flow direction. Alternatively, the membranes 16 and the spacers 18may be arranged to support various other air flow orientations, such ascounter-flow, concurrent flow, and the like.

FIG. 3 illustrates an end view of two adjacent layers 26 of the layerstack 202 (shown in FIG. 2) according to an embodiment of the presentdisclosure. The two layers 26 include three membrane panels 206 and twospacers 18 that separate the panels 206. The spacers 18 may each includeupstanding parallel walls 210 that define air channels 19 therebetween.For example, the spacers 18 may be oriented orthogonally to each othersuch that the walls 210 of the upper spacer 18B are orientedperpendicularly to the walls 210 of the lower spacer 18A. Air flow isconfigured to flow in the directions 220 and 222 through the airchannels 19 between the membrane panels 206. Direction 220 is shown toextend into the page, and direction 222 is shown to extend towards theright. Optionally, the directions 220, 222 may be reversed. The firstair stream 12 (shown in FIG. 1) may be configured to flow in thedirection 222, and the second air stream 14 (FIG. 1) may be configuredto flow in the direction 220. Sensible and latent energy may betransferred to or from the air streams in the direction of arrows 224through the membrane panels 206. The membrane panels 206 include amicroporous membrane (shown in FIG. 2) that is designed to maximize theamount of vapor that transfers across the membrane panels 206 whileminimizing the transfer of air across the panels 206.

FIG. 4 illustrates a magnified microporous membrane 16 of the energyexchange assembly 10 shown in FIG. 1, according to an embodiment. Inorder to balance the air permeability with vapor permeability (forexample, vapor diffusion resistance), the microporous membrane 16 mayhave a specific range of characteristics. For example, the microporousmembrane 16 may include various pores 402 that extend through the thinmembranes 16. The pores 402 may have a pore size or diameter 404 that isless than 0.5 micrometers (μm). In an embodiment, the pore size 404 ofthe pores 402 is between 0.01 and 0.4 μm. As used herein, the term“between” that introduces a range of values means “between andincluding” such that the range includes the listed end values. Morespecifically, the pore size 404 may be between 0.02 and 0.3 μm. Morespecifically, the pore size 404 may be between 0.04 and 0.2 μm, or morespecifically between 0.06 and 0.1 μm. The pore size 404 and/or range ofsizes is selected to reduce the vapor diffusion resistance of themembrane 16 to allow vapor transfer while also sufficiently reducing airpermeability through the membrane 16. In an embodiment, the shape of thepores 402 is not limited. For example, the pores 402 may be elliptical,as shown in FIG. 4, or may be rectangular, circular, or the like.

The microporous membrane 16 may have a porosity between 40% and 80%. Theporosity is the fraction or percentage of voids or empty spaces within amaterial. In an embodiment, the porosity of the microporous membrane 16may be between 45% and 80%. More specifically, the porosity may bebetween 50% and 75%, or more specifically between 55% and 70%.

In an embodiment, the microporous membrane 16 may have a membrane vapordiffusion resistance below 50 second/meters (sec/m) (measured using theDMPC method with the inlet air streams set to 5% relative humidity (RH)and 95% RH) and an air permeability below 0.08 ft³/min/ft² (0.041cm³/sec/cm²) at 0.5 inches of water (inH₂O) (based on ASTM D737)(approximately 125 Pa). More specifically, the membrane vapor diffusionresistance may be below 40 sec/m and the air permeability below 0.06ft³/min/ft² (0.03 cm³/sec/cm²) at 0.5 inH₂O. For example, the membranevapor diffusion resistance may be below 35 sec/m and the airpermeability below 0.0574 ft³/min/ft² (0.029 cm³/sec/cm²) at 0.5 inH₂O.

Referring now back to FIG. 2, the thickness of the microporous membrane16 also affects the rigidity and moisture vapor transfer rate (MVTR),which is directly related to the vapor diffusion resistance. Forexample, the rigidity of the membrane 16 increases by selecting athicker material with the same pore size and porosity. Howeverincreasing the thickness of the membrane 16 reduces the MVTR. Therefore,the thickness may be selected to achieve a balance between rigidity andMVTR. The thickness of the membrane 16 may be reduced while preservingrigidity by laminating the membrane 16 onto the backing layer (notshown). For example, the thickness of the membrane 16 may be less than50 μm, such as between 10 and 40 μm. More specifically, the thickness ofthe membrane 16 may be between 15 and 40 μm. When the membrane 16 isbonded to the backing layer, the thickness of the membrane panel 206 maybe between 100 and 400 μm, such as between 200 and 300 μm. The backinglayer may have higher pore sizes and porosities relative to themicroporous membrane 16, so the backing layer does not significantlyaffect (for example, has only a negligible impact on) vapor transmissionand/or air transmission through the membrane panel 206. In at least oneembodiment, the backing layer and the membrane 16 have a combinedstiffness (defined as the product of the modulus of elasticity and thematerial thickness) above 15 MPa·mm. More specifically, the stiffnessmay be above 25 MPa·mm.

As an example, a microporous membrane for use in an air-to-air energyrecovery core may be made out of polypropylene, with a pore size of 0.06μm, a porosity of 55%, and a thickness of 25 μm, and may be bonded it toa polyethylene mesh backing. The resulting membrane may have a vapordiffusion resistance of 28 sec/m, airflow permeability of 0.0146ft³/min/ft² (0.0074 cm³/sec/cm²) at 0.5 inches of water (inH₂O)(approximately 125 Pa), and a stiffness of 55 MPa·mm. When the resultingmembrane is used in the membrane panels of an energy exchange corehaving a size of 21 in.×21 in.×18.625 in. (53.3 cm×53.3 cm×47.3 cm) anda channel thickness of 3.5 mm, the resulting performance of the energyexchange core is a total effectiveness of 55% and an Outdoor AirCorrection Factor of 1.07 at a differential pressure of 5 inH₂O (basedon ASHRAE Standard 84) (approximately 1.244 kPa).

As another example, a microporous membrane for use in an air-to-airenergy recovery core may be formed of polypropylene, having a pore sizeof 0.1 μm, a porosity of 67%, and a thickness of 20 μm, and is bonded itto a 3.0 oz. (approximately 85 g) polypropylene spunbond non-wovenbacking. The resulting membrane has a vapor diffusion resistance of 17sec/m, airflow permeability of 0.0382 ft³/min/ft² (0.019 cm³/sec/cm²) at0.5 inH₂O, and a stiffness of 27 MPa·mm. When the resulting membrane isused in the same energy exchange assembly of size 21 in.×21 in.×18.625in. (53.3 cm×53.3 cm×47.3 cm) with a channel thickness of 3.5 mm, theresulting performance is a total effectiveness of 60% and an Outdoor AirCorrection Factor of 1.07 at a differential pressure of 2 inH2O (basedon ASHRAE Standard 84) (approximately 250 Pa).

FIG. 5 illustrates a graph 500 plotting vapor diffusion resistanceversus mean relative humidity for comparison between three membranes.The graph 500 compares a microporous membrane 502, as described herein,to other known membranes, including a non-porous hygroscopic membrane504 and a composite polymer membrane 506. As shown in FIG. 5, themicroporous membrane 502 may have less vapor diffusion resistance thanboth the non-porous hygroscopic membrane 504 and the composite polymermembrane 506. In addition, the microporous membrane 502 may have a low(or even negligible) dependency on humidity, as shown by the relativelack of a slope 508 in the trend line for the microporous membrane 502.The vapor diffusion resistance of the other two membranes 504, 506 maybe at least moderately dependent on humidity.

As seen in FIG. 5, the disadvantage of the non-porous hygroscopicmembrane 504 is that the ability for the membrane to transfer moistureis highly dependent on the relative humidity of the air. In a very humidenvironment, hygroscopic membranes have a low vapor diffusionresistance, while in a low humidity environment, the membranes have ahigh vapor diffusion resistance. This characteristic is shown by thedrastic slope 510 in FIG. 5 as the humidity increases.

One of the primary disadvantages of the composite polymer membrane 506is that by adding and bonding multiple polymer layers together, theresistance to moisture transfer through the membrane increases. Thus, asshown in FIG. 5, the vapor diffusion resistance is significantly higherthan that of the microporous membrane 502. Depending on the polymer filmused in the composite membrane 506, the vapor diffusion resistance mayalso be at least moderately dependent on the relative humidity of theair, as seen in FIG. 5 by the negative slope 512 of the trend line forthe composite membrane 506.

In addition, although not shown in FIG. 5, manufacturing the microporousmembrane as a single layer membrane with a supporting backing layer maybe cheaper to produce than typical multi-layer membranes. The typicalmulti-layer membranes either incorporate a hydrophobic or hydrophiliccoating or an additional second membrane layer in order to achieve lowwater vapor diffusion resistance and low air permeability. In anexemplary embodiment, the microporous membrane does not include anyadditional coating or layer, excluding the support backing which doesnot affect vapor diffusion or air permeability.

FIG. 6 illustrates a simplified schematic view of an energy exchangesystem 300 operatively connected to an enclosed structure 302, accordingto an embodiment of the present disclosure. The energy exchange system300 may include a housing 304, such as a self-contained module or unitthat may be mobile (for example, the housing 304 may be moved among aplurality of enclosed structures), operatively connected to the enclosedstructure 302, such as through a connection line 306, such as a duct,tube, pipe, conduit, plenum, or the like. The housing 304 may beconfigured to be removably connected to the enclosed structure 302.Alternatively, the housing 304 may be permanently secured to theenclosed structure 302. As an example, the housing 304 may be mounted toa roof, outer wall, or the like, of the enclosed structure 302. Theenclosed structure 302 may be a room of a building, a commoditiesstorage structure, or the like.

The housing 304 includes a supply air inlet 308 that connects to asupply air flow path 310. The supply air flow path 310 may be formed byducts, conduits, plenum, channels, tubes, or the like, which may beformed by metal and/or plastic walls. The supply air flow path 310 isconfigured to deliver supply air 312 to the enclosed structure 302through a supply air outlet 314 that connects to the connection line306. The supply air 312 may be received in the supply air flow path 310from the atmosphere (for example, an outside environment).Alternatively, the supply air 312 may be received from the enclosedstructure 302 as return supply air.

The housing 304 also includes a regeneration air inlet 316 that connectsto a regeneration air flow path 318. The regeneration air flow path 318may be formed by ducts, conduits, plenum, tubes, or the like, which maybe formed by metal and/or plastic walls. The regeneration air flow path318 is configured to channel regeneration air 320 received from theenclosed structure 302 to the atmosphere (for example, an outsideenvironment) through an exhaust air outlet 322. Alternatively, theregeneration air 320 may be received from the atmosphere and channeledback to the atmosphere through the exhaust air outlet 322.

As shown in FIG. 6, the supply air inlet 308 and the regeneration airinlet 316 may be longitudinally aligned. For example, the supply airinlet 308 and the regeneration air inlet 316 may be at opposite ends ofa linear column or row of ductwork. A separating wall 324 may separatethe supply air flow path 310 from the regeneration air flow path 318within the column or row. Similarly, the supply air outlet 314 and theexhaust air outlet 322 may be longitudinally aligned. For example, thesupply air outlet 314 and the exhaust air outlet 322 may be at oppositeends of a linear column or row of ductwork. A separating wall 326 mayseparate the supply air flow path 310 from the regeneration air flowpath 318 within the column or row.

The supply air inlet 308 may be positioned above the exhaust air outlet322, and the supply air flow path 310 may be separated from theregeneration air flow path 318 by a partition 328. Similarly, theregeneration air inlet 316 may be positioned above the supply air outlet314, and the supply air flow path 310 may be separated from theregeneration air flow path 318 by a partition 330. Thus, the supply airflow path 310 and the regeneration air flow path 318 may cross oneanother proximate to a center of the housing 304. While the supply airinlet 308 may be at the top and left of the housing 304, the supply airoutlet 314 may be at the bottom and right of the housing 304. Further,while the regeneration air inlet 316 may be at the top and right of thehousing 304, the exhaust air outlet 322 may be at the bottom and left ofthe housing 304.

Alternatively, the supply air flow path 310 and the regeneration airflow path 318 may be inverted and/or otherwise re-positioned. Forexample, the exhaust air outlet 322 may be positioned above the supplyair inlet 308. Additionally, alternatively, the supply air flow path 310and the regeneration air flow path 318 may be separated from one anotherby more than the separating walls 324 and 326 and the partitions 328 and330 within the housing 304. For example, spaces, which may containinsulation, may also be positioned between segments of the supply airflow path 310 and the regeneration air flow path 318. Also,alternatively, the supply air flow path 310 and the regeneration airflow path 318 may simply be straight, linear segments that do not crossone another. Further, instead of being stacked, the housing 304 may beshifted 90 degrees about a longitudinal axis aligned with the partitions328 and 330, such that that supply air flow path 310 and theregeneration air flow path 318 are side-by-side, instead of one on topof another.

An air filter 332 may be disposed within the supply air flow path 310proximate to the supply air inlet 308. The air filter 332 may be astandard HVAC filter configured to filter contaminants from the supplyair 312. Alternatively, the energy exchange system 300 may not includethe air filter 332.

An energy transfer device 334 may be positioned within the supply airflow path 310 downstream from the supply air inlet 308. The energytransfer device 334 may span between the supply air flow path 310 andthe regeneration air flow path 318. For example, a supply portion orside 335 of the energy transfer device 334 may be within the supply airflow path 310, while a regenerating portion or side 337 of the energytransfer device 334 may be within the regeneration air flow path 318. Inan alternative embodiment, the energy transfer device 334 or anadditional energy transfer device may be disposed within the supply airflow path 310 downstream of the energy exchange assembly 336 and withinthe regeneration air flow path 318 upstream of the energy exchangeassembly 336 in order to provide energy transfer between the supply air312 and the regeneration air 320. The energy transfer device 334 may bea desiccant wheel, a heat pipe, or a heat plate, for example. However,the energy transfer device 334 may be various other systems andassemblies, such as including liquid-to-air membrane energy exchangers(LAMEEs), as described below.

An energy exchange assembly 336, which may be formed as described abovewith respect to FIGS. 5-16, is disposed within the supply air flow path310 downstream from the energy transfer device 334. The energy exchangeassembly 336 may be positioned at the junction of the separating walls324, 326 and the partitions 328, 330. The energy exchange assembly 336may be positioned within both the supply air flow path 310 and theregeneration air flow path 318. As such, the energy exchange assembly336 is configured to transfer energy between the supply air 312 and theregeneration air 320.

One or more fans 338 may be positioned within the supply air flow path310 downstream from the energy exchange assembly 336. The fan(s) 338 isconfigured to move the supply air 312 from the supply air inlet 308 andout through the supply air outlet 314 (and ultimately into the enclosedstructure 302). Alternatively, the fan(s) 338 may be located at variousother areas of the supply air flow path 310, such as proximate to thesupply air inlet 308. Also, alternatively, the energy exchange system300 may not include the fan(s).

The energy exchange system 300 may also include a bypass duct 340 havingan inlet end 342 upstream from the energy transfer device 334 within thesupply air flow path 310. The inlet end 342 connects to an outlet end344 that is downstream from the energy transfer device 334 within thesupply air flow path 310. An inlet damper 346 may be positioned at theinlet end 342, while an outlet damper 348 may be positioned at theoutlet end 344. The dampers 346 and 348 may be actuated between open andclosed positions to provide a bypass line for the supply air 312 tobypass around the energy transfer device 334. Further, a damper 350 maybe disposed within the supply air flow path 310 downstream from theinlet end 342 and upstream from the energy transfer device 334. Thedamper 350 may be closed in order to allow the supply air 312 to flowinto the bypass duct 340 around the energy transfer device 334. Thedampers 346, 348, and 350 may be modulated between fully-open andfully-closed positions to allow a portion of the supply air 312 to passthrough the energy transfer device 334 and a remaining portion of thesupply air 312 to bypass the energy transfer device 334. As such, thebypass dampers 346, 348, and 350 may be operated to control thetemperature and humidity of the supply air 312 as it is delivered to theenclosed structure 302. Examples of bypass ducts and dampers are furtherdescribed in U.S. patent application Ser. No. 13/426,793, entitled“System and Method For Conditioning Air In An Enclosed Structure,” whichwas filed Mar. 22, 2012, and is hereby incorporated by reference in itsentirety. Alternatively, the energy exchange system 300 may not includethe bypass duct 340 and dampers 346, 348, and 350.

As shown in FIG. 6, the supply air 312 enters the supply air flow path310 through the supply air inlet 308. The supply air 312 is thenchanneled through the energy transfer device 334, which pre-conditionsthe supply air 312. After passing through the energy transfer device334, the supply air 312 is pre-conditioned and passes through the energyexchange assembly 336, which conditions the pre-conditioned supply air312. The fan(s) 338 may then move the supply air 312, which has beenconditioned by the energy exchange assembly 336, through the energyexchange assembly 336 and into the enclosed structure 302 through thesupply air outlet 314.

With respect to the regeneration air flow path 318, an air filter 352may be disposed within the regeneration air flow path 318 proximate tothe regeneration air inlet 316. The air filter 352 may be a standardHVAC filter configured to filter contaminants from the regeneration air320. Alternatively, the energy exchange system 300 may not include theair filter 352.

The energy exchange assembly 336 may be disposed within the regenerationair flow path 318 downstream from the air filter 352. The energyexchange assembly 336 may be positioned within both the supply air flowpath 310 and the regeneration air flow path 318. As such, the energyexchange assembly 336 is configured to transfer sensible energy andlatent energy between the regeneration air 320 and the supply air 312.

A heater 354 may be disposed within the regeneration air flow path 318downstream from the energy exchange assembly 336. The heater 354 may bea natural gas, propane, or electric heater that is configured to heatthe regeneration air 320 before it encounters the energy transfer device334. Optionally, the energy exchange system 300 may not include theheater 354.

The energy transfer device 334 is positioned within the regeneration airflow path 318 downstream from the heater 354. As noted, the energytransfer device 334 may span between the regeneration air flow path 318and the supply air flow path 310.

As shown in FIG. 6, the supply side 335 of the energy transfer device334 is disposed within the supply air flow path 310 proximate to thesupply air inlet 308, while the regeneration side 337 of the energytransfer device 334 is disposed within the regeneration air flow path310 proximate to the exhaust air outlet 322. Accordingly, the supply air312 encounters the supply side 335 as the supply air 312 enters thesupply air flow path 310 from the outside, while the regeneration air320 encounters the regeneration side 337 just before the regenerationair 320 is exhausted out of the regeneration air flow path 318 throughthe exhaust air outlet 322.

One or more fans 356 may be positioned within the regeneration air flowpath 318 downstream from the energy transfer device 334. The fan(s) 356is configured to move the regeneration air 320 from the regeneration airinlet 316 and out through the exhaust air outlet 322 (and ultimatelyinto the atmosphere). Alternatively, the fan(s) 356 may be located atvarious other areas of the regeneration air flow path 318, such asproximate to the regeneration air inlet 316. Also, alternatively, theenergy exchange system 300 may not include the fan(s).

The energy exchange system 300 may also include a bypass duct 358 havingan inlet end 360 upstream from the energy transfer device 334 within theregeneration air flow path 318. The inlet end 360 connects to an outletend 362 that is downstream from the energy transfer device 334 withinthe regeneration air flow path 318. An inlet damper 364 may bepositioned at the inlet end 360, while an outlet damper 366 may bepositioned at the outlet end 362. The dampers 364 and 366 may beactuated between open and closed positions to provide a bypass line forthe regeneration air 320 to flow around the energy transfer device 334.Further, a damper 368 may be disposed within the regeneration air flowpath 318 downstream from the heater 354 and upstream from the energytransfer device 334. The damper 368 may be closed in order to allow theregeneration air to bypass into the bypass duct 358 around the energytransfer device 334. The dampers 364, 366, and 368 may be modulatedbetween fully-open and fully-closed positions to allow a portion of theregeneration air 320 to pass through the energy transfer device 334 anda remaining portion of the regeneration air 320 to bypass the energytransfer device 334. Alternatively, the energy exchange system 300 maynot include the bypass duct 358 and dampers 364 and 166.

As shown in FIG. 6, the regeneration air 320 enters the regeneration airflow path 318 through the regeneration air inlet 316. The regenerationair 320 is then channeled through the energy exchange assembly 336.After passing through the energy exchange assembly 336, the regenerationair 320 passes through the heater 354, where it is heated, beforeencountering the energy transfer device 334. The fan(s) 356 may thenmove the regeneration air 320 through the energy transfer device 334 andinto the atmosphere through the exhaust air outlet 322.

As described above, the energy exchange assembly 336, which may beformed according to any of the methods described above, may be used withrespect to the energy exchange system 300. Optionally, the energyexchange assembly 336 may be used with various other systems that areconfigured to condition outside air and supply the conditioned air assupply air to an enclosed structure, for example. The energy exchangeassembly 336 may be positioned within a supply air flow path, such asthe path 310, and a regeneration or exhaust air flow path, such as thepath 318, of a housing, such as the housing 304. The energy exchangesystem 300 may include only the energy exchange assembly 336 within thepaths 310 and 318 of the housing 304, or may alternatively include anyof the additional components shown and described with respect to FIG. 6.

Embodiments of the present disclosure provide an energy exchangeassembly, such as an energy recovery core, that utilizes a microporousmembrane in membrane panels to increase the latent effectiveness of theassembly. The membrane panels may not require a hydrophilic layer ormultiple composite layers, other than a structural backing layer whichmay be added for support. The microporous membrane may not besignificantly dependent on the relative humidity of the air, whichallows the energy exchange assembly to have a similar effectiveness in ahot, humid climate and a cool, dry climate. The microporous membrane mayinclude many pores, which allow water vapor through the membrane. Thepore size of the pores may be designed to increase the water vaportransfer rate and reduce the vapor diffusion resistance. Some air mayalso pass through the pores across the membrane, but the amount ofairflow may be maintained at an acceptable level by optimizing theproperties of the membrane. For example, the properties of themicroporous membrane, such as pore size and porosity, may be designed toachieve a balance between optimizing vapor transfer while maintainingacceptable air leakage.

It is to be understood that the above description is intended to beillustrative, and not restrictive. For example, the above-describedembodiments (and/or aspects thereof) may be used in combination witheach other. In addition, many modifications may be made to adapt aparticular situation or material to the teachings of the variousembodiments of the disclosure without departing from their scope. Whilethe dimensions and types of materials described herein are intended todefine the parameters of the various embodiments of the disclosure, theembodiments are by no means limiting and are exemplary embodiments. Manyother embodiments will be apparent to those of skill in the art uponreviewing the above description. The scope of the various embodiments ofthe disclosure should, therefore, be determined with reference to theappended claims, along with the full scope of equivalents to which suchclaims are entitled. In the appended claims, the terms “including” and“in which” are used as the plain-English equivalents of the respectiveterms “comprising” and “wherein.” Moreover, the terms “first,” “second,”and “third,” etc. are used merely as labels, and are not intended toimpose numerical requirements on their objects. Further, the limitationsof the following claims are not written in means-plus-function formatand are not intended to be interpreted based on 35 U.S.C. §112(f),unless and until such claim limitations expressly use the phrase “meansfor” followed by a statement of function void of further structure.

This written description uses examples to disclose the variousembodiments of the disclosure, including the best mode, and also toenable any person skilled in the art to practice the various embodimentsof the disclosure, including making and using any devices or systems andperforming any incorporated methods. The patentable scope of the variousembodiments of the disclosure is defined by the claims, and may includeother examples that occur to those skilled in the art. Such otherexamples are intended to be within the scope of the claims if theexamples have structural elements that do not differ from the literallanguage of the claims, or if the examples include equivalent structuralelements with insubstantial differences from the literal languages ofthe claims.

What is claimed is:
 1. An energy exchange assembly, comprising: one ormore membrane panels, wherein the one or more membrane panels include amicroporous membrane that has a pore size between 0.02 and 0.3micrometers (μm) and a porosity between 45% and 80%.
 2. The energyexchange assembly of claim 1, further comprising a plurality of spacersthat define air channels configured to receive air streams therethrough,the one or more membrane panels each disposed between two spacers, theone or more membrane panels configured to allow a transfer of sensibleenergy and latent energy across the one or more membrane panels betweenthe air channels.
 3. The energy exchange assembly of claim 2, whereinthe plurality of spacers includes a first group of spacers and a secondgroup of spacers, the first group of spacers is orthogonally orientedwith respect to the second group of spacers.
 4. The energy exchangeassembly of claim 1, wherein the microporous membrane is devoid of atleast one of a hydrophilic or hydrophobic coating.
 5. The energyexchange assembly of claim 1, wherein the pore size of the microporousmembrane is between 0.04 and 0.2 μm.
 6. The energy exchange assembly ofclaim 1, wherein the porosity of the microporous membrane is between 50%and 75%.
 7. The energy exchange assembly of claim 1, wherein themicroporous membrane of the one or more membrane panels has a thicknessbetween 15 and 30 μm.
 8. The energy exchange assembly of claim 1,wherein the microporous membrane has a vapor diffusion resistance below40 seconds/meter (sec/m) and an air permeability below 0.06 ft³/min/ft².9. The energy exchange assembly of claim 1, wherein the one or moremembrane panels further include a backing layer bonded to themicroporous membrane for support, the one or more membrane panels havinga stiffness of at least 20 MPa·mm.
 10. The energy exchange assembly ofclaim 8, wherein the backing layer includes a non-woven mesh with alarger pore size and porosity than the microporous membrane, wherein thebacking layer does not significantly affect the transmission of vapor orair through the one or more membrane panels.
 11. The energy exchangeassembly of claim 1, wherein the microporous membrane is formed of atleast one of expanded polytetrafluoroethylene (ePTFE), polypropylene(PP), nylon, polyvinylidene fluoride (PVDF), or polyethersulfone (PES).12. An energy exchange system, comprising: a supply air flow pathconfigured to channel supply air to an enclosed structure; aregeneration air flow path configured to channel regeneration air fromthe enclosed structure to an outside environment; and an energy exchangeassembly disposed within the supply air flow path and the regenerationair flow path, wherein the energy exchange assembly comprises: aplurality of spacers; and a plurality of membrane panels, each membranepanel including a microporous membrane that has a pore size between 0.02and 0.3 micrometers (μm) and a porosity between 45% and 80%, whereineach of the spacers is positioned between two of the membrane panels todefine air channels through the spacer between the two membrane panels,the air channels configured to receive air streams therethrough, themembrane panels configured to allow a transfer of sensible energy andlatent energy across the membrane panels between the air channels. 13.The energy exchange system of claim 12, wherein the microporous membraneis devoid of at least one of a hydrophilic or hydrophobic coating. 14.The energy exchange system of claim 12, wherein the pore size of themicroporous membrane is between 0.04 and 0.2 μm.
 15. The energy exchangesystem of claim 12, wherein the porosity of the microporous membrane isbetween 50% and 75%.
 16. The energy exchange system of claim 12, whereinthe microporous membrane has a vapor diffusion resistance below 40seconds/meter (sec/m) and an air permeability below 0.06 ft³/min/ft².17. The energy exchange system of claim 12, wherein the plurality ofspacers includes a first group of spacers and a second group of spacers,the first group of spacers is orthogonally oriented with respect to thesecond group of spacers.
 18. The energy exchange system of claim 12,wherein the membrane panels further include a backing layer bonded tothe microporous membrane for support, the membrane panels having astiffness of at least 20 MPa·mm.
 19. The energy exchange system of claim18, wherein the backing layer includes a non-woven mesh with a largerpore size and porosity than the microporous membrane, wherein thebacking layer does not significantly affect the transmission of vapor orair through the membrane panels.
 20. The energy exchange system of claim12, wherein the microporous membrane is formed of at least one ofexpanded polytetrafluoroethylene (ePTFE), polypropylene (PP), nylon,polyvinylidene fluoride (PVDF), or polyethersulfone (PES).